In some areas of the United States well water contains appreciable iron which produces rust stains on buildings, side-walks and streets when used in lawn sprinkler systems. This is a longstanding problem in South Florida, where the water table is high and it is relatively economical for a property owner to use a shallow well pumping system for supplying the water needed to sprinkle the lawn. This economic advantage is offset for many property owners by the staining problem, so that in many cases "city water" is used for lawn sprinkling as well as in the house or other building. (The term "city water" is used herein to describe the water supplied to buildings by a municipality, county or private utility operating under the authority of the state Public Service Commission or similar public body.)
City water in many cases is relatively expensive because it has been treated to make it suitable for human ingestion, and sometimes for washing purposes, so as to eliminate impurities which are of no great consequence in lawn sprinkling. In coastal areas, excessive use of city water can threaten the city water supply with salt water intrusion, so that from an ecological standpoint it would be very advantageous to induce residents to stop using city water for lawn sprinkling purposes.